1. Field of the Invention
This invention is directed to a polyether-functional, liquid electrolyte, an epoxy curable electrolyte composition made from same and method for making both. More particularly, the liquid electrolyte is a hydrolytic condensation Product of aminosilane containing (i) at least one active amine group, and (ii) at least two hydrolyzable polyether groups attached to a silicon atom, wherein the product has some of the polyether groups attached to some of the silicon atoms.
2. Discussion of the Related Art
Electrochromic devices are devices in which a physical/chemical change produced in response to the induced electric field results in a change in the reflective or transmissive properties of the device with respect to electromagnetic radiations, e.g., UV, visible and IR radiations. Such devices generally include a film of electrochromic material and an ion-conductive insulating layer which functions as an electrolyte layer. The film and the electrolyte layer are in surface contact with each other for exchange of ions between the electrochromic film and the electrolyte layer. Two conductive electrode layers, at least one of them being transparent, are disposed on the opposite outer surfaces of the electrochromic material film and the electrolyte layer to provide means for applying a voltage across the Combined thickness of the electrochromic film and the electrolyte layer. The electrode layers are provided on substrates, which substrates may be of a material such as glass. Depending on the ion providing and ion storage capacity of ion conductive layer, a counter electrode located between ion conductive layer and electrode layer may be used. The electrodes are provided with external electrical leads connected to a voltage providing source.
The application of a voltage of proper polarity across the electrodes causes coloration of the electrochromic layer. By reversing the polarity of the applied voltage, the colored electrochromic layer will be uncolored (bleached). Changing from the bleached state to the colorless state or from the colored state to the bleached is termed "switching". The electrochromic material may be persistent in either its colored state or its non-colored state. By "persistent" is meant the ability of the material to remain, after removal of the electric field, in the absorptive state to which it is changed, as distinguished from a substantially instantaneous reversion to the initial state. The length of time a material is persistent is called its "open circuit memory" or simply "memory". Electrochromic devices of this type have been described for several uses, such as for image display, for light filtering, etc.
In such devices, the electrochromic film usually comprises an inorganic metal oxide material, most commonly a transition metal oxide, in particular tungsten oxide. When tungsten oxide is the electrochromic material, the electrolyte layer is adapted to provide a positively charged light metal cation, preferably, a proton or a lithium ion.
The electrolyte layer is generally a liquid electrolyte solution, typically based on sulfuric acid or lithium perchlorate in propylene carbonate. However, use of a liquid electrolyte has the inherent disadvantage associated with containment of a fluid. That is, it is required with liquid electrolytes used in layered electrochromic devices that the edges of the device be sealed so as to retain the liquid electrolyte. In addition, cell components such as the preferred tungsten oxide electrochromic material as well as certain electrode materials are attacked by acidic electrolyte materials, limiting the utility of strong acids for this application. Similar problems exist with gel electrolytes, such as the sulfuric acid-polyvinyl alcohol electrolyte gel.
Solid electrolytes form another class of electrolytes suggested for use in electrochromic devices. Solid electrolyte of complex halides are known, particularly iodides, of silver with alkali metal or quaternary ammonium ions, e.g., RbAg.sub.4 I.sub.5. Additionally, solid electrolytes may comprise aluminum compounds such as sodium beta-alumina and potassium beta-alumina. However, these electrolytes are all typically expensive to prepare and, in the case of the alumina compounds, could not be formed directly on components of an electrochromic device since they require very high processing temperatures. Others have suggested forming a solid electrolyte comprising a sheet of porous glass impregnated with a solid, ion-conductive silver or alkali metal compound One disadvantage of employing such an impregnated glass sheet is that, because it is a solid of limited flexibility, it would be difficult to assemble the component layers of an electrochromic device and achieve the intimate contact required between this sheet and the adjacent layers.
U.S. Pat. No. 4,250,074 to Foscante et al is directed to a modified epoxy coating composition comprising an interpenetrating polymer network of epoxy polymer and polysiloxane. It is disclosed therein that the network can be prepared by simultaneously reacting an epoxy resin with an aminosilane, water being substantially uniformly distributed throughout the mixture in an amount sufficient to bring about substantial hydrolytic polycondensation of the silane. The epoxy coating composition of the patent, in contrast to the present invention electrolyte, does not allow for polyether groups attached to the silicon atom.
It would be highly desirable to be able to provide a curable liquid electrolyte composition into an electrochromic device which, because it is initially a liquid when provided in the device, has the ability to intimately contact even irregularly shaped surfaces. It would be even more desirable if such a liquid electrolyte could be cured in place at room temperature in the device to form a solid electrolyte so as to avoid problems with its containment. It would be additionally desirable if the solid electrolyte would have an excellent ionic conductivity.
The aforementioned problems of prior art electrolytes are overcome by the curable liquid electrolyte of the present invention